clk: Fix slab corruption in clk_unregister()

When a clock is unregsitered, we iterate over the list of
children and reparent them to NULL (i.e. orphan list). While
iterating the list, we should use the safe iterators because the
children list for this clock is changing when we reparent the
children to NULL. Failure to iterate safely can lead to slab
corruption like this:

=============================================================================
BUG kmalloc-128 (Not tainted): Poison overwritten
-----------------------------------------------------------------------------

Disabling lock debugging due to kernel taint
INFO: 0xed0c4900-0xed0c4903. First byte 0x0 instead of 0x6b
INFO: Allocated in clk_register+0x20/0x1bc age=297 cpu=2 pid=70
 __slab_alloc.isra.39.constprop.42+0x410/0x454
 kmem_cache_alloc_trace+0x200/0x24c
 clk_register+0x20/0x1bc
 devm_clk_register+0x34/0x68
 0xbf0000f0
 platform_drv_probe+0x18/0x48
 driver_probe_device+0x94/0x360
 __driver_attach+0x94/0x98
 bus_for_each_dev+0x54/0x88
 bus_add_driver+0xe8/0x204
 driver_register+0x78/0xf4
 do_one_initcall+0xc4/0x17c
 load_module+0x19ac/0x2294
 SyS_init_module+0xa4/0x110
 ret_fast_syscall+0x0/0x48
INFO: Freed in clk_unregister+0xd4/0x140 age=23 cpu=2 pid=73
 __slab_free+0x38/0x41c
 clk_unregister+0xd4/0x140
 release_nodes+0x164/0x1d8
 __device_release_driver+0x60/0xb0
 driver_detach+0xb4/0xb8
 bus_remove_driver+0x5c/0xc4
 SyS_delete_module+0x148/0x1d8
 ret_fast_syscall+0x0/0x48
INFO: Slab 0xeec50b90 objects=25 used=0 fp=0xed0c5400 flags=0x4080
INFO: Object 0xed0c48c0 @offset=2240 fp=0xed0c4a00

Bytes b4 ed0c48b0: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a  ZZZZZZZZZZZZZZZZ
Object ed0c48c0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
Object ed0c48d0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
Object ed0c48e0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
Object ed0c48f0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
Object ed0c4900: 00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  ....kkkkkkkkkkkk
Object ed0c4910: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
Object ed0c4920: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
Object ed0c4930: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5  kkkkkkkkkkkkkkk.
Redzone ed0c4940: bb bb bb bb                                      ....
Padding ed0c49e8: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a  ZZZZZZZZZZZZZZZZ
Padding ed0c49f8: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
CPU: 3 PID: 75 Comm: mdev Tainted: G    B         3.14.0-11033-g2054ba5ca781 torvalds#35
[<c0014be0>] (unwind_backtrace) from [<c0012240>] (show_stack+0x10/0x14)
[<c0012240>] (show_stack) from [<c04b74a0>] (dump_stack+0x70/0xbc)
[<c04b74a0>] (dump_stack) from [<c00f7a78>] (check_bytes_and_report+0xbc/0x100)
[<c00f7a78>] (check_bytes_and_report) from [<c00f7c48>] (check_object+0x18c/0x218)
[<c00f7c48>] (check_object) from [<c00f7efc>] (__free_slab+0x104/0x144)
[<c00f7efc>] (__free_slab) from [<c04b6668>] (__slab_free+0x3dc/0x41c)
[<c04b6668>] (__slab_free) from [<c014c008>] (load_elf_binary+0x88/0x12b4)
[<c014c008>] (load_elf_binary) from [<c0105a44>] (search_binary_handler+0x78/0x18c)
[<c0105a44>] (search_binary_handler) from [<c0106fc0>] (do_execve+0x490/0x5dc)
[<c0106fc0>] (do_execve) from [<c0036b8c>] (____call_usermodehelper+0x134/0x168)
[<c0036b8c>] (____call_usermodehelper) from [<c000f048>] (ret_from_fork+0x14/0x2c)
FIX kmalloc-128: Restoring 0xed0c4900-0xed0c4903=0x6b

Fixes: fcb0ee6 (clk: Implement clk_unregister)
Cc: Jiada Wang <[email protected]>
Cc: Sylwester Nawrocki <[email protected]>
Cc: Kyungmin Park <[email protected]>
Signed-off-by: Stephen Boyd <[email protected]>
Signed-off-by: Mike Turquette <[email protected]>
Cc: [email protected]

drivers/clk/clk.c

@@ -2140,9 +2140,10 @@ void clk_unregister(struct clk *clk)
 
 	if (!hlist_empty(&clk->children)) {
 		struct clk *child;
+		struct hlist_node *t;
 
 		/* Reparent all children to the orphan list. */
-		hlist_for_each_entry(child, &clk->children, child_node)
+		hlist_for_each_entry_safe(child, t, &clk->children, child_node)
 			clk_set_parent(child, NULL);
 	}